Obesity is a known risk factor for vitamin D deficiency. Adequate levels of vitamin D are important, not only for bone health, but appear to be important for prevention of certain autoimmune diseases, infections and cancers. Current FDA recommendations for vitamin D intake do not differentiate between lean and obese people. There are no published studies indicating if the 25(OH)D response to a given daily dose of vitamin D is any less in an obese person than a normal weight person. The purpose of this study is to characterize the quantitative relationship between steady state cholecalciferol input and the resulting serum 25 (OH)D concentration in obese subjects. Data obtained in this study will be compared to published normative data for non-obese subjects. Recommendations will be provided for optimal treatment of vitamin D deficiency in obese men and women.